Semiconductor device and method therefor including multiple cap layers with amorphous layer

Abstract

A semiconductor crystal substrate includes a substrate, a first semiconductor layer including a nitride semiconductor and formed over the substrate, a second semiconductor layer including a nitride semiconductor and formed over the first semiconductor layer, a first cap layer formed on the second semiconductor layer, and a second cap layer formed on the first cap layer. Each of the first semiconductor layer and the second semiconductor layer has a single-crystal structure, the first cap layer has one of a single-crystal structure and a polycrystalline structure, and the second cap layer has an amorphous structure.

What is claimed is: 
     
       1. A semiconductor device, comprising:
 a substrate; 
 an electron transit layer including a nitride semiconductor and formed over the substrate; 
 an electron supply layer including a nitride semiconductor and formed over the electron transit layer; 
 a first cap layer formed on the electron supply layer; 
 a second cap layer formed on the first cap layer; 
 a source electrode formed over the electron supply layer; 
 a drain electrode formed over the electron supply layer; and 
 a gate electrode formed over the second cap layer, wherein 
 each of the electron transit layer and the electron supply layer has a single-crystal structure; 
 the electron supply layer includes a first surface facing the electron transit layer and a second surface opposite the first surface; 
 the first cap layer and the second cap layer are formed entirely of a same type of material; 
 the first cap layer has one of a single-crystal structure and a polycrystalline structure and is formed such that a first surface of the first cap layer directly contacts the second surface of the electron supply layer; 
 the second cap layer has an amorphous structure and is formed such that a first surface of the second cap layer contacts a second surface of the first cap layer that is opposite the first surface of the first cap layer directly contacting the second surface of the electron supply layer; and 
 the gate electrode directly contacts a second surface of the second cap layer that is opposite the first surface of the second cap layer. 
 
     
     
       2. The semiconductor device as claimed in  claim 1 , wherein the first cap layer and the second cap layer are formed of one of an oxide, a nitride, and an oxynitride. 
     
     
       3. The semiconductor device as claimed in  claim 1 , wherein the first cap layer and the second cap layer are formed of a material including AlN. 
     
     
       4. The semiconductor device as claimed in  claim 1 , wherein a thickness of the first cap layer is greater than or equal to 1 nm and less than or equal to 3 nm. 
     
     
       5. The semiconductor device as claimed in  claim 1 , wherein a thickness of the second cap layer is greater than or equal to 2 nm and less than or equal to 5 nm. 
     
     
       6. The semiconductor device as claimed in  claim 1 , wherein a thickness of the second cap layer is greater than a thickness of the first cap layer. 
     
     
       7. The semiconductor device as claimed in  claim 1 , wherein
 the electron transit layer is formed of a material including GaN; and 
 the electron supply layer is formed of a material including one of InAlN and InAlGaN. 
 
     
     
       8. A power-supply device comprising the semiconductor device of  claim 1 . 
     
     
       9. An amplifier comprising the semiconductor device of  claim 1 . 
     
     
       10. A manufacturing method of a semiconductor device, comprising:
 forming an electron transit layer including a nitride semiconductor and having a single-crystal structure over a substrate; 
 forming an electron supply layer including a nitride semiconductor and having a single-crystal structure over the electron transit layer; 
 forming a first cap layer having one of a single-crystal structure and a polycrystalline structure on the electron supply layer; 
 forming a second cap layer having an amorphous structure on the first cap layer; 
 forming a source electrode over the electron supply layer; 
 forming a drain electrode over the electron supply layer; and 
 forming a gate electrode over the second cap layer, wherein 
 the electron supply layer includes a first surface facing the electron transit layer and a second surface opposite the first surface; 
 the first cap layer and the second cap layer are formed entirely of a same type of material; 
 the first cap layer is formed such that a first surface of the first cap layer directly contacts the second surface of the electron supply layer; 
 the second cap layer is formed such that a first surface of the second cap layer contacts a second surface of the first cap layer that is opposite the first surface of the first cap layer directly contacting the second surface of the electron supply layer; and 
 the gate electrode is formed to directly contact a second surface of the second cap layer that is opposite the first surface of the second cap layer.